Abstract
The analysis and interpretation of the Dachaidan area, Qaidam Basin, is difficult, owing to the co-location of two groups of thrust faults (N–E faults and N–W faults) there and the area’s complicated structural deformation history. To address this problem, field geological investigation, seismic study, well logging, and drilling data were used to identify the key fault systems and their distribution patterns through the area. By integrating surface and subsurface structural features and seismic and non-seismic data, we carried out studies using structural modeling and analysis of the Dachaidan area. Study results identified two systems of thrust faults (N–W faults and W–E faults). We found that these faults could be categorized into three systems: a basin-margin thrust system, an intro-basin thrust system, and an intro-basin compression and strike-slip fault system. These systems showed different features in different areas and zones. We also constructed interpretation models of different deformation mechanisms in the basin and on basin margins. Three tectonic systems (compression, extension, and strike-slip) were identified, which were further divided into eight structural domains. We also established structure coexistence and distribution patterns. The overall structural character of the area was summarized as the northern and southern parts belonging to different zones, with the western and eastern parts belonging to different systems. By analyzing the SW–NE tectonic evolution sections, we defined the back-propagation structural evolution sequences of thrust nappes (on the basin margin or in the basin) and back-thrust structures (in the basin) as well as their influence on the residual Mesozoic strata.
Highlights
The Qaidam Basin is an important petroleum-producing basin in Northwest China (Jun et al, 2020)
The Qaidam Basin is the largest continental sedimentary basin in the northeast Qinghai– Tibet Plateau. It is separated from the Southern Qilian Mountain by a thrust fault zone at its northern boundary, from the Tarim Basin by the Altyn Tagh strike-slip fault zone in the west, and from the Eastern Kunlun orogenic belt and West Qinling orogenic belt by the Eastern Kunlun fault and Elashan Mountain Fault in the southwest and southeast (Jian et al, 2013; Meyer et al, 1998; Yin et al, 2002)
The complexity of the tectonic deformation at the north margin of the Qaidam Basin hinders the progress of oil-gas exploration in the region
Summary
The Qaidam Basin is an important petroleum-producing basin in Northwest China (Jun et al, 2020). A series of NW-striking low-angle thrust faults have developed inside the Yuka Depression under the action of the Sainan Fault thrust and the presence of a plastic Jurassic stratum, forming an enclosed area clamped between the Sainan and Southern Qilian Faults and controlling the formation of three major anticlinal zones, including the Mahaigaxiu zone. In Qaidam Mountain and the Lvliang piedmont, the Jurassic series form the hanging walls of thrusts, and the Yudong 1 and DY1 boreholes revealed the stratigraphic sequence expected in the autochthonous footwall sedimentation; (4) small-scale faulting was identified and characterized by analysis of drilling data. An imbricated thrust structure developed in the Middle Jurassic series, making the strata dip more steeply (40–75); multiple coal drill holes revealed a brecciated zone within the fault and that the fault surface features compression wrinkles and striations. The geological structural feature of bidirectional hedging was formed by the combined action of faults controlled by both the mountain and depression at the basin margin and in the basin and thrust faults
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